Basic annual PSD start battery maintenance 101.
  WARNING!!!!!
  The batteries in our trucks have enough power to weld wrenches and throw some serious sparks all over the place!
  Observe batteries for corrosion, dampness or water spray. The fluid on top of the battery is an indicator of overcharging or shorted cell. Look at the cables and check for corroded connectors or cables. Once the cables get corroded, its time to replace them.
  Remove batteries:
  Remove the ground (-) cables on both batteries to safely kill power to truck. Remove the positive (+) cables from both batteries. Remove the hold down clamps on both batteries. Remove both batteries from the truck. On the vans, the second battery is under the side cargo door, mounted on the frame rail in a metal battery box. The battery cables need to be disconnected from the frame rail to get enough slack to allow the battery box to be lowered. The box must be lowered to access the battery inside. I use a small jack to cradle the box and lower it after removing the bolts in the frame. Once the box is lowered the plastic lid needs to be removed to gain access to the battery inside.
  Clean batteries:
  I spray the batteries down with a degreaser and then hose down with a garden hose.  I also use a degreaser on the battery box and battery shelf followed with water from the hose. 
  Fill batteries:
  Take a flat blade screwdriver and remove the caps of the top of the cells. The fluid level should be between the vertical plate inside and the lowest level of the ring inside the cell. Bring the level of the acid up using distilled water, a commercial battery filler is the best tool for this purpose. It automatically shuts the flow of water when it gets to the right level.
  Clean terminals:
  I clean the battery posts and terminals with a round brush battery tool used for that purpose, and a shot of brake cleaner makes sure you get down to shiny metal on both surfaces. A wire brush on the connectors will help to remove any corrosion.
  Test Batteries:
  I use a commercial load tester to do a load test on each battery. The first part of the test measures the open circuit voltage. They should be somewhere between 12.2 and 12.6VDC. A reading of 2 volts less than the open circuit test indicate a shorted cell. DO NOT test the battery if you suspect a shorted cell, it may EXPLODE! The second part of the test places a load across the battery to test the condition of the battery. If you don’t have access to a load tester, you can and should take them to be tested. If either battery is weak, replace both of the batteries. Get the largest CCA battery that fit into your truck.
  Examine starter cables:
  This is the perfect time to do a complete exam of the cable at the starter. Due to high current and many heat cycles the connection needs to be absolutely perfect. I would recommend that the connection be removed cleaned to a shiny surface and re-installed. Make sure that you do a careful inspection of the ground side cables. They should be clean and tight. Now is the time to remove the connection and clean to make sure the connection is in good shape.
  Reinstall batteries:
  Once all the cleaning and prepping is done re-install the batteries and clamps.
  This is the part that will raise an eyebrow or two. I use a marine grade of bearing grease to seal the connections inside and out. Coat the post and connector with a light film where the lead is exposed. When the connecter is tightened onto the post the grease will squeeze out and seal the connection from the inside. Lead is very porous and will allow acid to creep up the posts from the inside causing corrosion. Be careful when tightening the bolts on the connector, this is an electrical connection NOT a mechanical connection. If the connection is too tight the lead will flow and become loose with heat cycles. 
  Take good care of your batteries and you will get longer life and a more dependable truck.
  Nick 99